The prelims are held around May-June.It has objective ie multiple choice questions. There are two papers (duration of each being 2 hrs). a) General studies and b)Optional subject: you can choose from Psychology, Sociology, Philosophy, Agriculture, Maths, Phy, Chem, Stats etc.
Important: It is not compulsory to choose the same subjects of your graduation. The results are declared in July-August and the successful candidates are called for the main examinations.
PS. The prelims score has no bearing for determining the final merit list for the services.

2. Main examination

The main written examination usually takes place in Oct-Nov, it comprises of 9
papers in all (a lot more strenuous than CAT!)
Duration of each paper is 3 hrs.
Language: one of the Indian languages, English, Essay GK and Current Affairs:
2 papers on general studies
Optionals: papers from two subjects that fall in optional-1 and two papers
from optional-2 (a choice of subjects is listed by the UPSC in the prospectus)
Candidates who are successful in the main examinations are eligible for an
interview which plays a crucial part in the selection.

The main written examination usually takes place in Oct-Nov, it comprises of 9 papers in all (a lot more strenuous than CAT!) Duration of each paper is 3 hrs.
Language: one of the Indian languages, English, Essay GK and Current Affairs: 2 papers on general studies
Optionals: papers from two subjects that fall in optional-1 and two papers from optional-2 (a choice of subjects is listed by the UPSC in the prospectus)
Candidates who are successful in the main examinations are eligible for an interview which plays a crucial part in the selection.

3. The Interview

The interview calls are sent in March-April of the following year and they
take place in the month of April-May. The Board of interviewers look for a
well-adjusted personality with the social traits, integrity and qualities
of leadership . PS. The number of candidates called for the interview is
normally twice the number of vacancies.

The interview calls are sent in March-April of the following year and they take place in the month of April-May. The Board of interviewers look for a well-adjusted personality with the social traits, integrity and qualities of leadership . PS. The number of candidates called for the interview is normally twice the number of vacancies.

Here is a list of subjects for IAS/UPSC exams. Under each subject is provided
reources regarding the subject that includes prelims and mains IAS syllabus as
well as question papers, strategy and suggested readings for the subject. The
IAS Syllabus and other services like the IPS and Income Tax is the same.